Ce(IV)-Based Metal-Organic Gel for Ultrafast Removal of Trace Arsenate from Water.

Abstract

As a potential replacement for metal-organic frameworks (MOFs), constructing metal-organic gels (MOGs) is an appealing but challenging topic since MOGs are a kind of shapeable MOF gels. Also, the rapid adsorption of trace heavy metal ions in aqueous media remains a serious challenge. Herein, a simple strategy for the synthesis of Ce(IV)-based metal-organic gel (Ce-MOG) was first developed for the rapid adsorption of trace As(V). The (NH4)2Ce(NO3)6 obtains hydroxide bridges after adding apposite NaOH, leading to [Ce6O4(OH)4]12+ clustering and inducing fast and excessive nucleation rates, which also leads to coordination disturbance of MOF nanocrystals to obtain Ce-MOG. The Ce-OH groups are the key to gel formation through hydrogen bonding and are the active site for the ultrafast adsorption of As(V). As expected, the resultant Ce-MOG has an excellent adsorption rate, making it possible to effectively decontaminate 500 ppb of As(V) to below the World Health Organization (WHO) recommended threshold for drinking water (10 ppb) within 1 min. It achieves equilibrium adsorption in 10 min, and the final arsenate-removing efficiency reaches 99.8%. For Ce-MOF, the effluent concentration of As(V) is higher than the drinking water standard, while equilibrium adsorption takes 60 min. The initial adsorption rate of Ce-MOG, h(k2qe2) is calculated and indicated to be 67.67 mg g-1 min-1, about 19.96 times that of Ce-MOF (3.39 mg g-1 min-1). As such, the excellent As(V) decontamination rate, selectivity, and reusability of Ce-MOG indicate its great potential for practical drinking water purification.